Recently, Light Emitting Diodes (LEDs) with long lifespan and low power consumption are being used in vehicle lamps, such as headlights, in place of traditional filament halogen lamps. A lighting control circuit is needed for adjusting the current flowing through an LED when the LED is employed as a light source due to the brightness of the LED being dependent on the size of current flowing through the LED.
There are descriptions of such lighting control circuits, for example the LED drive module described in JP-A-2009-231580 and the lighting control circuit described in JP-A-2006-114279.
A transistor is provided on the current path flowing to the LED in related circuits, such as the LED drive module of JP-A-2009-231580 and the lighting control circuit of JP-A-2006-114279, in which the current flowing to the LED is controlled by controlling current flowing in the transistor.
However, in the circuit configurations of JP-A-2009-231580 and JP-A-2006-114279, the higher the input voltage to the lighting control circuit, the greater the power loss in the transistor. Transistors in the foregoing circuit configurations have threshold power losses which are nominal values for the maximum power loss the terminal can withstand. However if the input voltage to the lighting control circuit is too high then concern arises of the power loss in the transistor exceeding this threshold power loss.